Fluid bearing

ABSTRACT

A fluid bearing for rotatably supporting a rotary shaft. A plurality of pressure generating zones are defined on a bearing surface of a bearing member in a circumferential direction. Each of the pressure generating zones comprises a pair of axially spaced fluid pockets, at least one raised land formed in at least one of the pair of fluid pockets, a passage member for fluidically communicating the pair of fluid pockets with each other, a throttle member connected to the fluid pockets for admitting pressurized fluid therein and an exhaust port formed on the raised land for discharging pressurized fluid. An exhaust member is formed on the bearing surface outside the pressure generating zones for discharging pressurized fluid.

This is a division, of application Ser. No. 53,038, filed June 28, 1979,now U.S. Pat. No. 4,285,551.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid bearing for supporting a rotaryshaft by means of a pressurized fluid.

2. Description of the Prior Art

In general, a bearing device for a spindle of a machine tool issubjected to an excessive load, such as vibration load, during machiningoperation. A bearing device depending on only a static bearing supportmay not be able to bear such excessive load. For this reason, there hasbeen required a fluid bearing capable of heightening bearing rigidityduring rotation of the spindle.

In a conventional fluid bearing, a hydrodynamic pressure generating zonewas formed on the bearing surface in addition to a hydrostatic pressuregenerating zone in order to increase the bearing rigidity duringrotation of the spindle. A typical example was such that a land portionwas formed within a fluid pocket. However, since the land portion wasformed within the fluid pocket, it was difficult to enlarge the area ofhydrodynamic pressure generating zone. It was also difficult toextremely decrease the diameter of a throttle formed on the fluid pocketfur supply of pressurized fluid in order to prevent the same from beingclogged by a foreign substance, and to increase the amount of fluid flowfrom the fluid pocket. For these reasons, the clearance between thespindle and the bearing surface had to be made larger than that of theusual plain bearing in order to get a throttle ratio required for properconstruction of the hydrostatic bearing which resulted in lowering thehydrodynamic effect.

In order to overcome this disadvantage, it has been considered toenclose the fluid pocket by exhaust grooves to increase the amount offluid flow so that the clearance between the spindle and the bearingsurface may be made smaller. However, according to this construction,the exhaust grooves communicating with atmosphere were formed axially ofthe bearing surface so that air was sucked into the bearing surface asthe spindle was rotated, resulting in cavitation. In particular, since aplurality of pressure generating zones, each being constituted by theexhaust grooves and the land portion, were arranged in thecircumferential direction, compressible fluid resulting from the mixtureof air was supplied to the land portions. Accordingly, hydrodynamicpressure was not as high as expected and thus whirling of the spindlebeing rotated at high speed was produced.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a new andimproved fluid bearing capable of heightening a hydrodynamic pressure.

Another object of the present invention is to provide a new and improvedfluid bearing capable of preventing air from being sucked into landportions thereof as the rotary shaft is rotated, whereby thehydrodynamic pressure is increased.

Another object of the present invention is to provide a new and improvedfluid bearing, wherein bearing rigidity in a rotational state of therotary shaft is higher than that in a stationary state.

A further object of the present invention is to provide a new andimproved fluid bearing capable of preventing bearing seizure even if therotary shaft continues to rotate due to its inertia immediately afterthe electric supply is interrupted and thus, supply of pressurized fluidis stopped.

Briefly, according to the present invention, these and other objects areachieved by providing a fluid bearing for rotatably supporting a rotaryshaft, as mentioned below. A bearing member is fixedly inserted in astationary housing and has an internal bore forming a bearing surface. Aplurality of pressure generating zones are defined on the bearingsurface in a circumferential direction. A pair of axially spaced fluidpockets are formed in each of the pressure generating zones. At leastone raised land is formed in at least one of the pair of fluid pockets.Passage means is provided for fluidically communicating the pair offluid pockets with each other. A throttle means is connected to thefluid pockets for admitting pressurized fluid therein. An exhaust portis formed on the raised land for discharging pressurized fluid and anexhaust means is formed on the bearing surface outside the pressuregenerating zones for discharging pressurized fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and many of the attendant advantages ofthe present invention will be readily appreciated as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a fluid bearing according tothe present invention;

FIGS. 2 and 3 are sectional views taken along lines II--II and III--IIIin FIG. 1, respectively;

FIGS. 4 and 5 show modifications of the embodiment shown in FIGS. 1 to3, wherein the clearance with the rotary shaft at the hydrodynamicpressure generating zone is made smaller than that at the hydrostaticpressure generating zone;

FIG. 6 shows the change in the hydrodynamic pressure at the hydrodynamicpressure generating zone in the circumferential direction;

FIG. 7 shows another modification, wherein the land portion is steppedinto two portions;

FIG. 8 shows change in the hydrodynamic pressure at the hydrodynamicpressure generating zone in the circumferential direction in themodification shown in FIG. 7;

FIG. 9 shows still another modification, wherein the land portion isseparated into two portions to form a wedge-shaped clearance with therotary shaft;

FIG. 10 is a longitudinal sectional view of another fluid bearingaccording to the present invention;

FIG. 11 is an enlarged sectional view of the bearing member on the sideof the grinding wheel shown in FIG. 10;

FIGS. 12 to 14 are sectional views taken along lines XII--XII toXIV--XIV in FIG. 11, respectively;

FIG. 15 is a schematic diagram showing the relationship between thesupports of the bearing members in a stationary state and a rotationalstate of the rotary shaft;

FIG. 16 is a longitudinal sectional view of another fluid bearingaccording to the present invention;

FIG. 17 is a sectional view taken along the lines XVII--XVII in FIG. 16;

FIG. 18 is a longitudinal sectional view of still another fluid bearingaccording to the present invention;

FIGS. 19 to 21, 23 and 25 are sectional views taken along the linesXIX--XIX to XXI--XXI, XXIII--XXIII and XXV--XXV in FIG. 18,respectively;

FIG. 24 is a sectional view taken along the lines XXIV--XXIV in FIG. 23;and

FIG. 26 is a sectional view taken along the lines XXVI--XXVI in FIG. 25.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals orcharacters refer to identical or corresponding parts throughout theseveral views, and more particularly to FIG. 1, there is shown a fluidbearing provided with a stationary housing 10 having an inner bore 10a,within which a bearing member 12 is fixedly inserted. The bearing member12 is provided with an inner bore or bearing surface 11 which is formedcoaxially with the bore 10a of the housing 10. The bearing surface 11provides rotatable support of a rotary shaft 13, subjected to a radialload at one end thereof, by means of pressurized fluid supplied into asmall clearance formed between the bearing surface 11 and the outersurface of the rotary shaft 13. As shown in dotted lines in FIG. 1, aplurality of pressure generating zones 14 are circumferentially arrangedon the bearing surface 11 of the bearing member 12. Each of the pressuregenerating zones 14 is provided with a pair of axially spaced fluidpockets 15 and 16, which are rectangular in shape and have the sameaxial width, a land portion 17 of the bearing surface 11 formed betweenthe pair of fluid pockets 15 and 16, and a supply groove 18 formed onthe land portion 17 in parallel relationship with the axis of thebearing member 12 for connecting one member of the fluid pocket 15 andone member of the fluid pocket 16.

On the middle of the supply groove 18, a supply port 19 is formed andextends to the outer periphery of the bearing member 12, as shown inFIG. 2. A throttle member 20 having a small throttle bore 20a isinterposed in the supply port 19. The supply port 19 communicates withan annular groove 21 formed on the outer periphery of the bearing member12. The annular groove 21 communicates, in turn, with a supply passage24 formed on the bearing housing 10, so as to receive pressurized fluidfrom a pressure fluid supply pump [not shown]. A pair of annular exhaustgrooves 22 and 23 are formed on the bearing surface 11 outside thepressure generating zones 14 so as to form annular land portions 15a and16a of the bearing surface 11 between the same and the fluid pockets 15and 16, respectively. The annular land portions 15a and 16a serve asresistance against flow of pressurized fluid. Small raised lands 15b and16b forming a small clearance with the rotary shaft 13, as shown in FIG.3, are circumferentially arranged within the pockets 15 and 16,respectively. Exhaust ports 25 and 26 are formed on the respective smallraised lands 15b and 16b. The exhaust groove 22 and the exhaust ports 25communicate with an exhaust passage 27 formed on the housing 10, whilethe exhaust groove 23 and the exhaust ports 26 communicate with anexhaust passage 28 formed on the housing 10. The exhaust passages 27 and28 are connected through the atmosphere to a reservoir (not shown). Theabove-described fluid pockets 15 and 16 serve as a hydrostatic pressuregenerating zone, while the land portion 17 serves as a hydrodynamicpressure generating zone.

The land portion 17 and the annular land portions 15a, 16a of thebearing surface 11 and the small raised lands 15b, 16b are formed in acircular shape in cross section with the same radius and axis. Thediameter of the rotary shaft 13 is formed to be uniform in the axialdirection so as to have the same clearance with both the hydrostaticpressure generating zone and the hydrodynamic pressure generating zone.

In operation, when pressurized fluid is supplied into the supply passage24 from the supply pump (not shown) under the state that the rotaryshaft 13 is not rotated, this pressurized fluid is admitted from theannular groove 21 through each of the throttle bores 20a of the throttlemembers 20 and the supply grooves 18 into the respective fluid pockets15 and 16 to form a fluid film between the rotary shaft 13 and thebearing surface 11. Pressurized fluid within the fluid pockets 15 and 16is exhausted from the exhaust grooves 22 and 23 and the respectiveexhaust ports 25 and 26 through the clearance formed between the rotaryshaft 13 and the annular land portions 15a, 16a and the small raisedlands 15b, 16b into the exhaust passages 27 and 28. As a result,hydrostatic pressure depending upon the flow resistance or the clearanceat the annular land portions 15a, 16a and the small raised lands 15b,16b is generated at the hydrostatic pressure generating zonesconstituted by the fluid pockets 15 and 16 to support the rotary shaft13.

Since each of the land portions 17 is enclosed by the fluid pockets 15and 16 and the supply groove 18 to restrict fluid flow therefrom, theland portion 17 also generates hydrostatic pressure.

When the rotary shaft 13 is rotated in a direction as indicated by anarrow A in FIG. 2, pressurized fluid supplied into each of the supplypassages 18 is sucked and introduced into the clearance between each ofthe land portions 17 and the rotary shaft 13 to thereby generatehydrodynamic pressure which is higher than the hydrostatic pressure.

Since only the supply passages 18 supplied with pressurized fluid arearranged in the circumferential direction of the land portions 17, airis not sucked in the land portions 17 as the rotary shaft 13 is rotated,which results in an increase in the hydrodynamic pressure.

FIGS. 4 and 5 show modifications of the embodiment shown in FIGS. 1 to3, wherein the clearance with the rotary shaft 13 at the hydrodynamicpressure generating zone is made smaller than that at the hydrostaticpressure generating zone in order to increase the hydrodynamic pressure.In FIG. 4, the diameter of the rotary shaft 13b at the hydrodynamicpressure generating zone is formed to be larger than that 13a at thehydrostatic pressure generating zone, while the diameter of the bearingsurface 11 of the bearing member 12 is uniform in the axial direction.In FIG. 5, the diameter of the bearing surface at the hydrodynamicpressure generating zone is formed to be smaller than that at thehydrostatic pressure generating zone, while the diameter of the rotaryshaft 13 is uniform in the axial direction.

By forming the clearance with the rotary shaft 13 at the hydrodynamicpressure generating zone to be smaller than that at the hydrostaticpressure generating zone, hydrodynamic pressure at the hydrodynamicpressure generating zone changes in the circumferential direction, asshown in FIG. 6.

FIG. 7 shows another modification in order to further increase thehydrodynamic pressure. The land portion 17 is stepped into two portions17a and 17b in the circumferential direction. The land portion 17b isformed in a circular shape in cross section to have the same radius andaxis with the annular land portions 15a, 16a and the small raised lands15b, 16b. The land portion 17a, surrounded by the pair of fluid pockets15, 16 and the supply groove 18, is also formed in a circular shape incross section and has the same axis with the land portion 17b. However,the radius of the land portion 17a is a little larger than that of theland portion 17b.

By forming the land portion 17 into two stepped land portions 17a and17b, the hydrodynamic pressure changes in the circumferential direction,as shown in FIG. 8. It is seen that from FIG. 8 that the hydrodynamicpressure is maximum at the stepped point 17c.

FIG. 9 shows still another modification for increasing the hydrodynamicpressure. The land portion 17 is separated into two portions 17b and 17din the circumferential direction. The land portion 17b is formed in acircular shape in cross section to have the same radius and axis withthe annular land portions 15a, 16a and the small raised lands 15b, 16b,as in the modification in FIG. 7. However, the radius of the landportion 17d is gradually decreased in the rotational direction A of therotary shaft 13 with respect to the axis of the land portion 17b, and issmoothly connected to the land portion 17b to form a wedge-shapedclearance with the rotary shaft 13.

Another embodiment of the present invention will now be described withreference to FIGS. 10 to 14. As shown in FIG. 10, a pair of bearingmembers 112a and 112b are inserted into a stationary housing 110 fromthe opposite ends. The bearing members 112a and 112b are provided withinner bores or bearing surfaces 111a and 111b, respectively, forrotatably supporting a rotary shaft 113. The rotary shaft 113 is formedat its central portion with an enlarged portion 130, the opposite sidesof which constitute thrust bearings with the inner ends of the bearingmembers 112a and 112b. A detailed description of the thrust bearings isomitted since they do not relate to a subject matter of the presentinvention. One end of the rotary shaft 113 near the bearing member 112acarries a grinding wheel 131 and the other end of the rotary shaft 113near the bearing member 112b supports a pulley 132. Since theconstruction of the bearing member 112a is similar to that of thebearing member 12 shown in FIG. 1, only the differences therebetween isdescribed.

As shown in FIGS. 11 to 14, the axial width of each rectangular fluidpocket 115, which is remote from the inner end 133 of the bearing member112a, is smaller than that of each rectangular fluid pocket 116 which isnear the inner end 113 of the bearing member 112a. Small raised lands116b are circumferentially arranged only within each of the fluidpockets 116. Each of axial passages 118 for connecting the fluid pockets115 and 116 is formed within the bearing member 112a at a position awayfrom the bearing surface 111a so that a land portion 117 is in anannular form. A supply port 119 is formed within each of the fluidpockets 116 and extended to the outer periphery of the bearing member112a. With this arrangement, the land portion 117 of the bearing member112a is located more adjacent to the grinding wheel 131 from the axialcenter of the bearing member 112a.

The bearing member 112b on the pulley side has the same construction asthat of the bearing member 112a with respect to the fluid pockets 115,116, the small raised lands 116b, the land portion 117, the axialpassages 118 and the supply ports 119. Therefore, the land portion 117of the bearing member 112b is located more adjacent the pulley 132 fromthe axial center of the bearing member 112b.

FIG. 15 is a schematic diagram showing the relationship between thesupports of the bearing members 112a and 112b in a stationary state anda rotational state of the rotary shaft 113. In the stationary state ofthe rotary shaft 113, hydrostatic pressure is generated over the entireaxial widths of the bearing members 112a and 112b, so that supportpoints S of the bearing members 112a and 112b are almost at the axialcenters thereof. A distance between the support points S is representedas l2.

In the rotational state of the rotary shaft 112, hydrodynamic pressure,which is higher than hydrostatic pressure, is generated at the landportions 117 which are located outwardly from the axial centers of thebearing members 112a nad 112b. Accordingly, support points D of thebearing members 112a and 112b in the rotational state are locatedoutwardly by Δl from the support points S in the stationary state, suchthat the span between the support points D is larger than that betweenthe support points S. Therefore, bearing rigidity in the rotationalstate is higher than that in the stationary state.

Assuming that load W is applied to the rotary shaft 113 at a point A,which is spaced a distance l1 from the support point S of the bearingmember 112a, displacement Xs of the rotary shaft 113 at the point A inthe state is expressed as follows: ##EQU1## where Ks=rigidity due onlyto hydrostatic pressure.

When the rotary shaft 113 is rotated, hydrodynamic pressure isgenerated, resulting in increasing the rigidity from Ks into Kd andmoving the support points from S into D. Accordingly, displacement Xd ofthe rotary shaft 113 at the point A in the rotationary state isexpressed as follows: ##EQU2##

It is understood by comparison of the equations (1) and (2) that thedisplacement Xd is much smaller than Xs, since Kd and l1/l2 are largerthan Ks and ##EQU3## respectively. Accordingly, rigidity in therotational state is much larger than that in the stationary state.Furthermore, when the load W is applied to the rotary shaft 113 at thepoint A, displacement h_(d) at the support point D of the bearing member112a is always larger than displacement h_(s) at the support point S,whereby bearing sensitivity in the rotational state is increased.

Referring now to FIGS. 16 and 17, it is assumed that a rotary shaft 213subjected to a radial load F at its one end is rotated in a direction A.An axial passage 218 connecting fluid pockets 215 and 216, which arelocated in the direction of the load F, is formed at a lower position inthe gravitational direction. With this arrangement, even if a pressurefluid supply pump is stopped due to interruption of electric supply andthus generation of hydrostatic pressure disappears, a portion of fluidremains in the axial passage 218. Accordingly, even if the rotary shaft213 continues to rotate due to its inertia immediately after stoppage ofthe supply pump, the remaining fluid in the axial passage 218 issmoothly introduced into a land portion 217 as indicated in dotted linesin FIG. 16, so that bearing seizure due to a lack of lubricating fluidmay be prevented.

With respect to the fluid pockets 215, 216 and the axial passage 218,which are located in the direction opposite to that of the load F, theremaining fluid in the axial passage 218 formed at an upper position inthe gravitational direction is moved toward the fluid pockets 215 and216 due to its gravity and thus is not smoothly introduced into the landportion 217. However, this portion does not bear the load F, so thatthere is no fear of bearing seizure due to a lack of lubricating fluid.

Another embodiment of the present invention will now be described withreference to FIGS. 18 to 26. As shown in FIG. 18, a pair of bearingmembers 312a and 312b are inserted into a stationary housing 310 fromopposite ends. The bearing members 312a and 312b are provided with innerbores or bearing surfaces 311a and 311b, respectively, for rotatablysupporting a rotary shaft 313. One end of the rotary shaft 313 near thebearing member 312a carries an angular type grinding wheel 331 and theother end of the rotary shaft 313 near the bearing member 312b supportsa pulley 332.

As shown in dotted lines in FIG. 18, a plurality of pressure generatingzones 314 are circumferentially arranged on each of the bearing surfaces311a and 311b. Each of the pressure generating zones 314 is providedwith a U-shaped fluid pocket 333 constituted by a pair of axially spacedfluid pockets 315 and 316 and an axially extending passage 318connecting the pair of fluid pockets 315 and 316, a land portion 317 ofthe bearing surface formed between the pair of fluid pockets 315 and316, a plurality of small raised lands 315b formed within the U-shapedfluid pocket 333, an exhaust port 325 formed on each small raised land315b and connected to atmosphere and a supply port 319 for introducingpressurized fluid into the U-shaped fluid pocket 333 through a throttlemember 320.

A pair of annular exhaust grooves 322 and 323 are formed outside thepressure generating zones 314. The annular exhaust groove 322 of thebearing member 312a located outwardly near the grinding wheel 331communicates with one end of an axial passage 334 formed within thebearing member 312a at the lowermost position in the gravitationaldirection. The other end of the axial passage 334 communicates withatmosphere through a passage 327 formed within the bearing housing 310.The inner annular exhaust groove 323 of the bearing member 312acommunicates with one end of a radial passage 335 formed within thebearing member 312a at the uppermost position in the gravitationaldirection. The other end of the passage 335 communicates withatmosphere. Each exhaust port 325 communicates with each aixal passage336, which in turn communicates with an annular groove 337 formed on theouter periphery of the bearing member 312a. The annular groove 337communicates with atmosphere through an axial passage 338 formed withinthe bearing housing 310 at the uppermost position in the gravitationaldirection.

As shown in FIGS. 23 and 24, the axial passage 318 of the bearing member312a connecting the fluid pockets 315 and 316, which are located in thedirection of a load F1, is formed at a lower position in thegravitational direction. The load F1 is defined as a result of theweight of the grinding wheel 331 and belt tension on the pulley 332,which is applied on the bearing member 312a when the rotary shaft 313continues to rotate due to its inertia after stoppage of a pressurefluid supply pump. As shown in FIGS. 25 and 26, the axial passage 318 ofthe bearing member 312b connecting the fluid pockets 315 and 316, whichare located in the direction of a load F2, is formed at a lower positionin the gravitational direction. The load F2 is defined as a result ofthe weight of the grinding wheel 331 and the belt tension on the pulley332, which is applied on the bearing member 312b when the rotary shaft313 continues to rotate due to its inertia after stoppage of thepressure fluid supply pump.

In operation, fluid exhausted into the inner annular exhaust grooves 323and exhaust ports 325 is discharged from the openings at the uppermostposition in the gravitational direction. Accordingly, the grooves 323and ports 325 are usually filled with fluid so that air is notintroduced therefrom into the bearing surfaces 311a and 311b duringrotation of the rotary shaft 313, thus resulting in an increase inbearing rigidity.

Moreover, even if the pressure fluid supply pump is stopped due tointerruption of electric supply, the grooves 323 and ports 325 serve asa reservoir to store fluid so as to prevent bearing seizure due to lackof lubricating fluid.

Furthermore, even if the rotary shaft 313 continues to rotate due to itsinertia immediately after stoppage of the pressure fluid supply pump,fluid in the axial passages 318 located in the direction of the loads F1and F2 is smoothly introduced into the land portions 317, as indicatedin dotted lines in FIGS. 24 and 26, so that bearing seizure due to lackof lubricating fluid may be prevented.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A fluid bearing for rotatably supporting arotary shaft comprising:a stationary housing; a pair of bearing membersfixedly and coaxially inserted in said housing from the opposite endsthereof, each bearing member having an internal bore which forms abearing surface; a plurality of pressure generating zones defined oneach of said bearing surfaces in a circumferential direction; a pair ofaxially spaced fluid pockets in each of said pressure generating zones,an axial width of one of said pair of fluid pockets which is locatedremote from the axially inner end of each bearing member being smallerthan that of the other fluid pocket located near the inner end of eachbearing member; at least one raised land formed in at least one of saidpair of fluid pockets in each of said pressure generating zones; passagemeans for fluidically communicating said pair of fluid pockets with eachother; throttle means connected to said fluid pockets for admittingpressurized fluid in the same; an exhaust port formed on said raisedland for discharging pressurized fluid; and exhaust means formed on eachof said bearing surfaces outside said pressure generating zones fordischarging pressurized fluid.
 2. A fluid bearing as claimed in claim 1,wherein said at least one raised land is formed in the other fluidpocket in each of said pressure generating zones.